The tissues in the human oral cavity are generally exposed to repeated low doses of known or suspected carcinogens, such as alcohol, tobacco smoke, and x-radiation from diagnostic medical and dental radiology. The proposed study would examine the effects of concurrent, repeated exposures to low doses of x-radiation on tumor induction by repeated, low dose applications of a chemical carcinogen (DMBA), in established carcinogenic amounts, on an in vivo mammalian oral epithelial cell renewal system. Previous synergistic cocarcinogenesis studies of this type have been limited to relativelyy high radiation levels, and estimates of effects from low radiation doses have been generally arrived at through extrapolation from high dose data. Young adult male Syrian golden hamsters receive multiple applications of 0.1% DMBA in mineral oil to the right cheek pouch, 2OR x-radiation to the head and neck, or both agents simultaneously. Tumor incidence, onset latency, histopathology, cytokinetics, and hemodynamics are evaluated. Results thus far have suggested synergy between the two agents. It is anticipated that the results of these experiments will provide information leading to some clarification of mechanisms involved in he interaction between concurrent exposures to low levels of x-radiation and chemical carcinogens, as well as provide a useful model system and preliminary data for more detailed quantitative studies of low level exposures to multiple carcinogens and factors which modify host responses to these exposures. BIBLIOGRAPHIC REFERENCES: Lurie, A. G. and Matteson, S. R.: 99mTc-diphosphonate bone imaging and uptake in healing rat extraction sockets. J. Nuc. Med., 17:688-692, 1976. Lurie, A. G., Puri, S., James, R. B. and Jensen, T. W.: Radionuclide bone imaging in the surgical treatment planning of odontogenic keratocysts. J. Oral Surg., 42:726-733, 1976.